Over one quarter of the adult population experiences sleep and circadian disturbances, characterized by inadequate sleep duration, poor sleep quality, the presence of sleep disorders and non-optimal timing of sleep. Non-white racial groups, Hispanic/Latinos and adults with fewer socioeconomic resources have a higher burden of sleep and circadian disturbances than their counterparts. Limitations of these prior studies include cross-sectional study designs, self-reported sleep, and incomplete assessment of sleep and circadian rhythms. The objective of our study is to identify a set of modifiable factors that explain racial disparities in sleep and circadian disturbances between black and white middle-aged adults. We will additionally test whether these sleep and circadian disparities account for disparities in blood pressure control. Our overall hypothesis is that black participants have a greater burden of adverse health behaviors, adiposity, psychological and social stressors, and environmental insults at the neighborhood and household level that contribute to more sleep and circadian disturbances as compared with whites. To accomplish our goal, we will conduct an ancillary study in 2,500 adults (45% black and 60% women) aged 53-65 years old at the upcoming 35-year follow-up examination of the Coronary Artery Risk Development in Young Adults (CARDIA) study. All participants will undergo wrist actigraphy for 7 days, obstructive sleep apnea severity (OSA) determined using an in-home screening device, and sleep behaviors, diagnoses of sleep disorders and sleep quality via questionnaire. In a subset of 1,000 participants from the Chicago and Birmingham field centers, we will assess the neighborhood and household environment using a combination of secondary sources (e.g., traffic data), questionnaires and recording devices to capture household noise, light and temperature. We will combine these newly collected data with the wealth of information that will be determined in the core CARDIA examination and that has been collected in a standardized manner across 8 prior examinations. The Specific Aims of our study are as follows: 1) Determine the contribution of behavioral, psychosocial, and clinical characteristics over 35 years on racial disparities in sleep and circadian disturbances in middle-age; 2) Identify environmental factors associated with racial disparities in 7-day average and intra-individual variability (day-to-day changes) in sleep duration and quality; and, 3) Quantify the contribution of sleep and circadian disturbances on racial disparities in blood pressure levels in the estimated 60% of participants with hypertension. We will additionally explore whether sex as a biological variable modifies the hypothesized associations across all Aims. Our proposed study is a timely acknowledgement of the significance of sleep to racial disparities in cardiovascular health. We anticipate that our findings will have a sustained impact on a broad set of stakeholders, including clinicians, researchers, policymakers and middle-aged adults who are looking for intervention targets to reduce racial disparities in sleep and circadian rhythms that will promote cardiovascular health equity.